Embodiments of the invention relate generally to current sensors and, more particularly, to an apparatus for sensing electrical current flowing through a conductor.
Electrical switching apparatus, such as circuit interrupters, relays, and motor soft starters, often include one or more current sensor configured to measure the current flowing through the electrical switching apparatus. Known current sensors include a current transformer with a matching current meter, a ferrite toroid with matching current meter or printed circuit board assembly, and a Rogowski coil and matching circuit board assembly.
Alternatively, the electrical switching apparatus may include magnetic field sensors that measure current using similar principles as a transformer—namely, a magnetic field is induced around a conductor as current is passed through the conductor. This magnetic field is induced into a magnetic core constructed of a core material that can range from a highly magnetic material such as ferrous magnetic iron or steel, or a very weak magnetic material such as air. A second coil is looped around the magnetic coil material or around the current carrying member. The amount of current induced into the second coil is used to determine the current flowing through the conductor.
Each of the aforementioned current sensors includes a physical limitation that is a major disadvantage in constructing a compact electrical switching apparatus. Transformer, toriod, or Rogowski coil sensors often require bulky mounting brackets. The second coil or ferrite core of magnetic field sensors must be positioned about the periphery of the conductor of interest and results in an undesirable increase in the overall package size of the electrical switching apparatus. Further, in multi-phase devices such as a three phase motor starter that includes separate, closely spaced conductors, the potential for cross-talk, or interference between the current sensors becomes quite high.
In addition to being susceptible to external magnetic fields, present magnetic field current sensors are also limited in their sensing range and resolution. While some known sensors incorporate a corresponding circuit to amplify the output signals of the magnetic field sensors and achieve greater sensing range and higher resolution, there is room for improvement in the sensing range of magnetic field sensors.
Accordingly, it would be desirable to have a current sensor assembly that has a wide sensing range and enhanced resolution. It would further be desirable for such a current sensor assembly to provide improved immunity to external magnetic fields.